d. mallants, d. jacques, j. Šimůnek, and m.th. van genuchten

1

HP1: A coupled numerical code for variably saturated water flow, solute

transport and biogeochemical reactions in soils and sediments

D. Mallants, D. Jacques, J. Šimůnek, and M.Th. van Genuchten

2

HP1: HYDRUS1D-PHREEQC Possibilities of the code Benchmarking

PCE-dissolution Migration of decay chain of adsorbing contaminants during

precipitation/evaporation Illustration of ‘coupled’ effects

TNT degradation under steady state flow Cd leaching in an acid podzol: lysimeter experiments Long-term transient flow and transport of major cations and heavy metals

in a soil profile U-transport in agricultural field soils

Outline

3



precipitation/evapotranspiration Illustration of ‘coupled’ effects

TNT degradation under steady state flow Cd leaching in an acid podzol: lysimeter experiments Long-term transient flow and transport of major cations and heavy

metals in a soil profile U-transport in agricultural field soils

4

Simulation Tool

A Coupled Numerical Code forVariably Saturated Water Flow,

Solute Transport andBiogeochemistryin Soil Systems

Simulating water flow, transport and bio-geochemical reactions in environmental soil quality problems

Biogeochemical modelPHREEQC-2.4

Flow and transport modelHYDRUS-1D 2.0

5

Coupling procedure

Coupling method: non-iterative sequential approach (weak coupling)

Within a single time step: First solve water flow equation (HYDRUS)

Second: solve heat transport equation Then solve convection-dispersion equation for

solute transport for element master/primary species (inert transport) (HYDRUS)

Finally solve for each element, calculate speciations, equilibrium reactions, kinetic reactions, … (PHREEQC)

6




TNT degradation under steady state flow Cd leaching in an acid podzol: lysimeter experiments Long term transient flow and transport of major cations and heavy metals


7

1D FE water flow in variably-saturated media 1D FE transport of multiple solutes by CDE 1D heat transport Mixed equilibrium / kinetic biogeochemical reactions

Aqueous speciation (reactions in pore-water) Cation exchange (on clay, organic matter, …) Surface complexation (e.g. iron oxyhydroxides) Mineral dissolution / precipitation Any kinetic reactions (oxidation/reduction,

(bio)degradation, dissolution/precipitation)

HP1 – model features

8

HP1 examples

Transport of heavy metals (Zn2+, Pb2+, and Cd2+) subject to multiple cation exchange

Transport with mineral dissolution of amorphous SiO2 and gibbsite (Al(OH)3)

Heavy metal transport in a medium with a pH-dependent cation exchange complex

Infiltration of a hyperalkaline solution in a clay sample (kinetic precipitation-dissolution of kaolinite, illite, quartz, calcite, dolomite, gypsum, …)

Long-term transient flow and transport of major cations (Na+, K+, Ca2+, and Mg2+) and heavy metals (Cd2+, Zn2+, and Pb2+) in a soil profile.

Kinetic biodegradation of TNT (multiple degradation pathways)

9

Cycling of radionuclides/metals in soil-plant systems Heterogeneous physical/chemical properties Water flow under rainfall - evapotranspiration

conditions Root growth and water uptake Microbiological growth Degradation of organic matter with

radionuclide/metal release Transport/adsorption/decay Uptake of radionuclides/metals by plants

Typical application and processes involved

10


PCE-dissolution under steady-state flow conditions Migration of decay chain of adsorbing contaminants during


TNT degradation under steady state flow Cd leaching in an acid podzol: lysimeter experiments Long-term transient flow and transport of major cations and heavy metals


11

Test I: PCE degradationPCE degradation pathway

(Schaerlaekens et al., Hydrological Processes, 1999)

PCE, TCE: organic contaminant Solvent, degreasing agent, dry-cleaning

VC: vinylchloride: carcinogenic

Perchloroethylene Trichloroethylene

12

Test I: PCE degradationComparison with analytical solution

0 10 20 30D istance (m )

0

0.2

0.4

0.6

0.8

1

Con

cent

ratio

n (m

ole

/ l)

A nalytica l so lu tion(Sun e t a l., 2004)H P 1

PCE

TC E

0 10 20 30D istance (m )

0

0.05

0.1

0.15

0.2

0.25

Con

cent

ratio

n (m

ole

/ l)

cis-DC E

trans-D C E

1,1-DC E

13

Test II: Migration of decay chain species

Problem definition Three contaminants (Cont_a, Cont_b, Cont_c)

First-order degradation

Cont_a Cont_b Cont_c

Linear (Cont_a)/ nonlinear Freundlich (Cont_b, Cont_c) sorption Homogeneous soil profile (Soil covered with grass (rooting depth 20 cm)) Atmospheric boundary conditions (time dependent) HP1 comparison with HYDRUS-1D

nF = 1 nF = 0.9 nF = 0.8

µ1= 0.005 d-1 µ2= 0.06 d-1 µ3= 0.02 d-1

14

Test II: Migration decay chain species

Water flow boundary conditions

0 1 2 3T im e (d )

0

50

100

150

200

Cum

ulat

ive

flux

(cm

/ m

²)P

T p

E p

T a

E a

P - E p

P - E a

(y)

15

Test II: Migration decay chain speciesWater content profiles

0.05 0.1 0.15 0.2 0.25 0.3 0.35w ater content

-100

-80

-60

-40

-20

0

Dep

th (c

m)

H YD R US -1DH P1

225 d 465 d

630 d

840 d

1096 d

16

Test II: Migration decay chain speciesConcentration-depth profiles

0 0.5 1 1.5 2 2.5C onta (m ole / l)

-100

-80

-60

-40

-20

0

Dep

th (c

m)

225 d

465 d630 d

840 d

1096 d

0.00 0.02 0.04 0.06 0.08 0.10 0.12C ontb (m ole / l)

-100

-80

-60

-40

-20

0

Dep

th (c

m)

225 d

465 d

630 d

840 d

1096 d

H YD R US-1DH P1

BC: Step-function input for Cont_a (1 M) & Cont_b (0.1 M)Leaching

Breakthrough

17

0 20 40 60 80 100D e p th (cm )

0

0.2

0.4

0.6

0.8

1

Con

cent

ratio

n (m

ol/l)

0 20 40 60 80 100D e p th (cm )

0

0.02

0.04

0.06

0.08

0.1

Con

cent

ratio

n (m

ol/l)

0 20 40 60 80 100D e p th (cm )

0

0.02

0.04

0.06

0.08

0.1

Con

cent

ratio

n (m

ol/l)

H Y D R US -1DH P 1

Conta

Contb

Contc

250 d500 d

1000 d

Test II: Migration decay chain species

Concentration-time profiles

Excellent agreement between HP1 and HYDRUS Performance criterion for HP1 becomes more strict: Pe×Cr < 0.4

18




TNT degradation under steady-state flow Cd leaching in an acid podzol: lysimeter experiments Long-term transient flow and transport of major cations and heavy metals


19

Transport of TNT and its Daughter Products

•Soil profile: 100 cm, loam, Ks=1 cm/h, 10 days•TNT in top 5 cm of soil: 1 mg/kg (6.61e-6 mol)•TNT dissolution: rate = 4.1 mg/cm2/hour (1.8e-5 mol/cm2/hour)•Solid 2ADNT at equilibrium with solution, 2ADNT solubility = 2,8 g/L Sorption (instantaneous)

Adsorption coefficients Kd [L/kg]:•TNT 3•2ADNT 5•4ADNT 6•TAT 0

Degradation•TNT -> 66% is transformed in 2ADNT and 34% is to 4ADNT Transformation constants [1/hour]•TNT 0.01•2ADNT 0.006•4ADNT 0.04

4ADNTTNT TAT

2ADNT

20

Transport of TNT and its Daughter Products

0

20

40

60

80

1000.E+00 1.E-07 2.E-07 3.E-07 4.E-07

Concentration [mol/L]

Dep

th [c

m]

2 d

4

6

8

10

0

20

40

60

80

1000.E+00 2.E-09 4.E-09 6.E-09 8.E-09 1.E-08 1.E-08


Dep

th [c

m]

2 d

4

6

8

10

2ADNT

0

20

40

60

80

1000.E+00 3.E-09 5.E-09


Dep

th [c

m]

2 d4

6

8

10

4ADNT

0

20

40

60

80

1000.E+00 3.E-09 5.E-09


Dep

th [c

m] 2 d

4 6 810

TAT

TNT

•This example indicates that ground water may be more vulnerable to leaching of TNT daughter products (notably TAT) than of the parent compound itself, and that monitoring for the daughter products may provide an early warning of possible TNT leaching.

21

Cd leaching in acid podzol Introduction

Nothern region of Belgium: historical contamination of soils with Cd, Pb, Cu, Zn by atmospheric deposition originated from the non-ferro industry (historical contamination, beginning 20th century)

Risk of flooding with water containing increased salt concentrations

22

Cd leaching in acid podzol Objectives

To describe the leaching of major cations, Zn and Cd from a lysimeter after application of an increased salt concentration (tracter test)

To assess the effect of increased salt concentrations (CaCl2) on Cd leaching using a new coupled reactive transport model HP1

23

Cd leaching in acid podzol Problem definition (Seuntjens et al., 2000)

Podzol soil (Kempen) contaminated with heavy metals (Cd, Zn, Pb)

Lysimeter (80-cm-diameter, 100-cm-long)

Equipped with TDR probes Bottom: grid based wick sampler system Displacement exp.: boundary conditions

Time (d) CaCl2 (mol/l)0-27.9 0.00527.9-28.9 0.05 (tracer)28.9-80 0.005

Bh2

AE

C1

C2

CEC (meq/kg)24.411.783.962.914.47.4

Bh1

24

Cd leaching in acid podzol Leaching experiment set-up

Leachate collectors

TDR probes

Cable

tester

25

Components in solution: H, Ca, Na, K, Mg, Al, Cl, Br, Cd, Zn

Speciation reactions in soil solution Complexation reactions of Zn, Cd with

OH-, Cl-:

Cd(OH)+, Cd(OH)2, Cd(OH)3-, Cd(OH)3

2-

Cd(Cl)+, Cd(Cl)2, Cd(Cl)3-, Cd(Cl)3

2-

Cd leaching in acid podzol Leaching experiment modelling (1)

26

Ion exchange reactions (solid phase interaction) Half reactions (X-: exchange complex):

H+ + X- = HX Ca2+ + 2 X- = CaX2

H, Ca, Na, K, Mg, Cd, Zn Equilibrium constants are adapted to fit the

measurements (site-specific Log_K values)

Equilibrium with gibbsite (Al(OH)3)

Cd leaching in acid podzol Leaching experiment modelling (2)

27

Cd leaching in acid podzol Multi-component modelling results (1)

0 20 40 60 80T im e (d)

3

4

5

6

pH

0 20 40 60 80T im e (d)

0

1

2

3

4

Al (m

mol/l)

0 20 40 60 80T im e (d)

0

5

10

15

20

Cl (m

mol/

l)

0 20 40 60 80T im e (d)

0

1

2

3

4

5

Ca (m

mol/l)

28


0 20 40 60 80T im e (d)

0

0.25

0.5

0.75

1

Na

(mm

ol/l)

0 20 40 60 80T im e (d )

0

0.1

0.2

0.3

K (m

mol

/l)

29


0 20 40 60 80T im e (d )

0x10 0

2x10 - 3

4x10 - 3

6x10 - 3

8x10 - 3

1x10 - 2

Cd

(mm

ol/l)

0 20 40 60 80T im e (d)

0x10 0

1x10 - 1

2x10 - 1

3x10 - 1

Zn (m

mol

/l)

30


0 20 40 60 80T im e (d )

0x10 0

2x10 - 3

4x10 - 3

6x10 - 3

8x10 - 3

1x10 - 2

Cd

(mm

ol/l)

0 20 40 60 80T im e (d )

0x10 0

1x10 0

2x10 0

3x10 0

4x10 0

Ca

(mm

ol/l)

pulse 0 .05 M CaC l2 - com plexation/com petition

31

Cd leaching in acid podzol Cd remobilisation due to complex

formation

0 20 40 60 80T im e (d )

0x10 0

2x10 - 3

4x10 - 3

6x10 - 3

8x10 - 3

1x10 - 2

Cd

(mm

ol/l)

0 20 40 60 80T im e (d )

0x10 0

1x10 0

2x10 0

3x10 0

4x10 0

Ca

(mm

ol/l)

pulse 0 .05 M CaC l2 - com plexation/com petition

0 20 40 60 80T im e (d)

0x10 0

2x10 - 3

4x10 - 3

6x10 - 3

8x10 - 3

1x10 - 2

Cd

(mm

ol/l)

0 20 40 60 80T im e (d)

0x10 0

1x10 0

2x10 0

3x10 0

4x10 0

Ca

(mm

ol/l)

pulse 0 .05 M CaC l2 - com plexation/com petitionpulse 0 .005 C aC l2 - less com plexation/com petition

0 20 40 60 80T im e (d )

0x10 0

2x10 - 3

4x10 - 3

6x10 - 3

8x10 - 3

1x10 - 2

Cd

(mm

ol/l)

0 20 40 60 80T im e (d )

0x10 0

1x10 0

2x10 0

3x10 0

4x10 0

Ca

(mm

ol/l)

pulse 0 .05 M CaC l2 - com plexation/com petitionpulse 0 .005 CaC l2 - less com plexation/com petitionpulse 0 .05 C aBr2 - com petition (no com plexation)

CdCln2-n

Complexation or competition?

Complexation!

32

Cd leaching in acid podzol Conclusion

Increased Cd mobilization due to exchange Ca-Cd complexation with Cl- (most important)

Geochemical speciation models required (instead of e.g. Kd approach)

HP1: allows for transient flow conditions

33




TNT degradation under steady state flow Cd leaching in an acid podzol: lysimeter experiments Long term transient flow and transport of major cations and heavy metals


34

Geochemical transport under transient variably-saturated flow

Cycling of metals in soil-plant systems Heterogeneous physical/chemical properties Water flow under rainfall - evaporation

conditions Root growth and water uptake Metal transport/adsorption/speciation Uptake of metals by plants Degradation of organic matter with metal

release

35

steady-state

actual surface flux

= P-ETact

potential surface flux

= P-ETpot

0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8T im e (year)

0

100

200

300

Cum

ulat

ive

infil

trat

ion

(cm

)

Long-term transient flow and transport Transient infiltration at surface

Bh1

AE

Bh2C1

C2

36

Long-term transient flow and transport Effect of transient infiltration on Cd migration

Site 1

Site 2

Site 6

...

O rganic M atter

C ation Exchange

Aqueous Specia tion

W ater P hase A ir Phase

HKHM g

C a

C d

HN aHH

C a

Zn

H

HHHHHHHHH

H +

H +

ZnC l2

H +

H +

H +N a +

C d 2+

H +

B r -

O H -

H +

C l-

C dC l+

H +

N aO H

H +

H +H +

H +

K +

H +

H +

Z n 2+

Geochemical Reactions: Multisite cation exchange

2 3 4 5 6p H

0

0.01

0.02

0.03

0.04

0.05

Neg

ativ

e ch

arge

orga

nic

mat

ter

(meq

/g s

oil) A -horizon

E-horizon

Podzol soil•Multi-site exchange complex•CEC: organic matter•CEC=f(pH)•Complex formation: Cl-metals•Variable infiltration

37

Long-term transient flow and transport Cd mobility and bio-availability as function of

, pH, Cl- (1)

pH

1975 1976 1977 1978Time (year)

-6

-4

-2

0

De

pth

(c

m)

3

3.2

3.4

3.6

3.8

4

4.2

4.4

Time (year)

Water Content

1975 1976 1977 1978

-6

-4

-2

0

De

pth

(c

m)

0.02

0.06

0.1

0.14

0.18

0.22

0.26

Log(Aqueous Cd) (mmol/kg soil)

1975 1976 1977 1978Time (year)

-6

-4

-2

0

De

pth

(c

m)

-6.6

-6.2

-5.8

-5.4

-5

-4.6

-4.2

-3.8Log(Cl) (mmol/kg soil)

1975 1976 1977 1978Time (year)

-6

-4

-2

0

De

pth

(c

m)

-2.3

-2

-1.7

-1.4

-1.1

-0.8

38

Long-term transient flow and transport Cd mobility and bio-availability as function of

, pH, Cl- (2)

Bh1Bh2

AE

C1

C2

0.2

0.24

0.28

0.32

0.36

0.4

Wat

er c

onte

nt3

3.5

4

4.5

5

pH

pH

Water Content

1972 1974 1976 1978 1980 1982Time (year)

Cl

Aqu

eou s

Cd

Cd

Cl10-4

10-5

10-6

10-2

10-3

39

Long-term transient flow and transportConclusions

Temporal variability of physical soil variables (θ) results in temporal variability in geochemical variables (pH, Cl-,…)

Applied to heavy metal mobility and bio-availability: Water content variations linearly related to pH

and inversely to Cl- variations pH inversely related to dissolved metal

concentration (multi-site cation exchange f(pH)) Cl- concentration linearly related to dissolved

metal concentration (complex formation)

40




TNT degradation under steady state flow Cd leaching in an acid podzol Long term transient flow and transport of major cations and heavy metals


41

Motivation: assessment of post-closure safety for surface repository Inherent uncertainties, especially for the long-term Use of multiple lines of reasoning Complementary safety indicators for evaluating

and confirming safety: e.g., RN fluxes, U-concentration

Objective: estimate long-term U-leaching from agricultural soils, compare with U-fluxes from planned surface repository

Introduction / objectives (1)

42

Introduction / objectives (2) Multiple lines of reasoning

[U]radwaste

[U]concrete, mine waste

U-flux from NF

U-flux from soil, host formation

Individual dose

Dose limit, dose constraint

43

• Introduction

• A new biogeochemical transport code:HP1

• Problem statement: soil, geochemical reactions, BC/IC

• Simulation results

• U-fluxes from soil vs. surface repository

• Conclusions

44

Problem statement (1)Multilayered soil profile

Dry Podzol,7 horizons All horizons characterized

Thickness Unsaturated hydraulic properties pH Organic matter content Fe2O3 content

AE

Bh1Bh2

Bh/C

C 1

C 2

07

19

2428

50

75

depth(cm )

Sim

ulat

ion

dept

h: 1

m

0 0 . 4 0 . 8 1 . 2 1 . 6 2I r o n c o n t e n t ( % )

0 1 2 3 4 5O rganic matter (%)Source: Seuntjens et al., 2001. J. Contam. Hydrol.

45

Aqueous speciation reactions Chemical components: C, Ca, Cl, F, H, K, Mg,

N(5), Na, O(0), O(-2), P, S(6), U(6)

Multi-site cation exchange reactions Related to amount of organic matter Increases with increasing pH

Surface complexation reactions Specific binding to charged surfaces (FeOH) Related to amount of Fe-oxides

Problem statement (2)Geochemical equilibrium reactions

46

Problem statement (3)Multi-site cation exchange reactions

Because more groups of humic and fulvic acids dissociate as pH ↑proton selectivity decreases when pH ↑

negative charge of organic matter ↑

Site 1

Site 2

Site 6

...

O rganic M atter

C ation Exchange

A queous S peciation

W ater Phase A ir Phase

HKHM g

C a

C d

HN aHH

C a

Zn

H

HHHHHHHHH

H +

H +

ZnC l2

H +

H +

H +N a +

C d 2+

H +

B r -

O H -

H +

C l-

C dC l+

H +

N aO H

H +

H +H +

H +

K +

H +

H +

Zn 2+

Log_K1 (HY)

Log_K2 (HY)

Log_K6 (HY)

...

UO22+

UO22+

UO2Cl+

UO2OH+

47

Problem statement (4)pH-dependent negative charge

2 3 4 5 6p H

0

0.01

0.02

0.03

0.04

0.05N

egat

ive

char

geor

gani

c m

atte

r(m

eq /

g so

il) A -horizon

E-horizon

U-species accounted for:• UO2

2+, UO2OH+, UO2Cl+, UO2F+, UO2H3PO42+, ...

Based on Appelo et al., 1998. Appl. Geoch.

adsorbs

48

Problem statement (5)Surface complexation

• Surface complexation model 0.875 reactive sites/mol Fe (Waite et al., 1994. G.C. Acta) Surface complex: FeOUO2

+ (Dzombak & Morel, 1990) • Changing processes in U adsorption with increasing pH

2 3 4 5 6pH

0

20

40

60

80

100

% U

(VI)

adso

rbed Tota l

C EC

SC

Increased deprotonationIncreased U-sorption

U-species replaced by other cations

49

Initial condition No U initially present in soil profile (<> few 10 Bq/kg)

Boundary condition 200-year time series of synthetic meteorological data

to calculate preciptiation and potential evaporation Composition rain water from measurements P-fertilizer (Ca(H2PO4)2): ~3000 Bq 238U/kg

Applied each year on May 1 (1 g P/m2) 1.610-1 mol Ca(H2PO4)2 /m² in 1 cm of rain =>3.810-6 mol U /m2 in 1 cm of rain (~105 Bq/ha)

Problem statement (6)Initial and Boundary conditions

50

• Introduction





• Conclusions

51

0.0x10 0 8.0x10 - 4 1.6x10 - 3

C a (m o l / 1 0 0 0 cm ³ so il)

5 0

4 0

3 0

2 0

1 0

0

Dep

th (c

m)

0.0x10 0 1.0x10 - 3 2.0x10 - 3 3.0x10 - 3

P (m o l / 10 0 0 cm ³ so il)

5 0

4 0

3 0

2 0

1 0

0

Dep

th (c

m)

0.0x10 0 2.0x10 - 9 4.0x10 - 9

U (m o l / 1 00 0 cm ³ so il)

100

75

50

25

0

Dep

th (c

m)

100 year150 year200 year

(b) (d) (f)

Simulation results (1)Total Ca, P, and U depth profiles

Steady-state

Transient

• Ca, P, U accumulation in Bh-horizon (rich in o.m. & Fe-ox.)• U-breakthrough after 100 y• U moved faster under transient than under steady-state

52

Simulation results (2)Transient flow conditions =>

transient geochemical conditions

150 151 152 153 154 155 156 157 158 159 160Tim e (ye a r)

3.4

3.6

3.8

4

4.2pH

S teady-sta te

A tm ospheric

5 cm depth

• Water content variations induce pH variations (dry soil => low pH)• pH variations => variations in sorption potential (low pH => low sorption)

53

Simulation results (3)∆pH results in time variations of

U-mobility

3.4 3.6 3.8 4 4.2p H

1x10 1

1x10 2

1x10 3

1x10 4

K =

ads

orbe

d U

(mol

/l) /

aque

ous

U (m

ol /

l)

A tm osphericS teady-sta te 25 cm depth

5 cm depth

•At least one order of magnitude variation in K

54

Simulation results (4)U-fluxes: steady-state vs. transient

0 50 100 150 2001x10 - 6

1x10 - 3

1x10 0

1x10 3

1x10 6

U fl

ux (B

q ye

ar-1

ha-

1 )

0 50 100 150 2001x10 - 6

1x10 - 3

1x10 0

1x10 3

1x10 6

U fl

ux (B

q ye

ar-1

ha-

1 )

0 50 100 150 200Tim e (ye a r)

1x10 - 6

1x10 - 3

1x10 0

1x10 3

1x10 6

U fl

ux (B

q ye

ar-1

ha-

1 )

0 50 100 150 2001x10 - 6

1x10 - 3

1x10 0

1x10 3

1x10 6

0 50 100 150 200T im e (year)

1x10 - 6

1x10 - 3

1x10 0

1x10 3

1x10 6

7 cm

19 cm

29 cm

50 cm

100 cm

▲ : steady-state▬ : transient

Long-term U flux = U application rate:~105 Bq/ha/y

E-horizon

55

• Introduction





• Conclusions

56

Comparison of U-fluxes

Planned Belgian surface repository :

70 000 m3 LILW; ~71012 Bq long-lived alphas Flux from NF, optimistic scenario: ~3 Bq/ha/y 238U Flux from NF, realistic scenario: ~103 Bq/ha/y 238U

Fertilizer application: ~103 -104 Bq/ha/y 238U

(1) Drums & monolith(2) Module(3) Soil cover(4) Drainage gallery

57

• Introduction





• Conclusions

58

Conclusions (1)

New biogeochemical transport code HP1 provides useful insight into complex U-migration processes

U migration under atmospheric boundary conditions faster than under steady-state flow conditions Due to changing flow and geochemical

conditions (∆ pH =>∆ sorption) Atmospheric boundary conditions important

when assessing U-flux to groundwater

59

Conclusions (2)

Calculated U-fluxes from soil same order of magnitude as U-flux from surface repository

Limitations of the study No interactions U-nitrate CO2 transport not accounted for More typical agricultural soils Include plant uptake Need verification experiments ...

60

Use of Geochemical Transport Models

Process Coupling and InteractionsTools for investigating the impacts of multiple coupled biogeochemical reactions in the presence of complex flow fields and spatial heterogeneity. Enable extrapolation to environmentally relevant temporal and spatial scales.

Interpretation of Laboratory and Field DataProvide a useful framework for interpreting experimental results. Serve as a tool for understanding qualitative and quantitative trends and relationships present in the data.

Sensitivity AnalysisPermit the systematic evaluation of the impact of model parameters (both reactive and hydrogeological), initial conditions, and boundary conditions upon the model output.

Integration and SynthesisTool for integrating all of the knowledge obtained from simulation, sensitivity analyses, and laboratory and field experimentation.

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